Gas sensors are arranged in an exhaust pipe of an internal combustion engine and used to sense a specific gas concentration in exhaust gas flowing in the exhaust pipe. In the gas sensors, a sensor structural body, which is formed by stacking a heater on a sensor element, is held by a holder; a distal end portion of the sensor structural body is protruded from the holder so as to be exposed to a measured gas. The heater is provided to heat a solid electrolyte body and electrodes provided on the solid electrolyte body to a sensor activation temperature. Specifically, the heater is formed by providing an electric conductor layer on a ceramic substrate; the electric conductor layer generates heat when supplied with electric current. Moreover, in the sensor element, there are formed: a pump cell that adjusts the oxygen concentration in the exhaust gas which is the measured gas; and a sensor cell for sensing the specific gas concentration of the measured gas whose oxygen concentration has been adjusted by the pump cell.
For example, a gas sensor element disclosed in Patent Document 1 has a heater portion which includes a heat-generating element that generates heat when supplied with electric current. Moreover, in Patent Document 1, it is disclosed that the heater voltage is regulated so as to have the relationship between heater resistance and heater electric power satisfying a heater control function, thereby controlling the temperature of the gas sensor element.